Bidirectional Transepithelial Water Transport: Measurement and Governing Mechanisms

Abstract

In the search for the mechanisms whereby water is transported across biological membranes, we hypothesized that in the airways, the hydration of the periciliary fluid layer is regulated by luminal-to-basolateral water transport coupled to active transepithelial sodium transport. The luminal-to-basolateral (JWL-->B) and the basolateral-to-luminal (JWB-->L) transepithelial water fluxes across ovine tracheal epithelia were measured simultaneously. The JWL-->B (6.1 microliter/min/cm2) was larger than JWB-->L (4.5 microliter/min/cm2, p < 0.05, n = 30). The corresponding water diffusional permeabilities were PdL-->B = 1.0 x 10(-4) cm/s and PdB-->L = 7.5 x 10(-5) cm/s. The activation energy (Ea) of JWL-->B (11.6 kcal/mol) was larger than the Ea of JWB-->L (6.5 kcal/mol, p < 0.05, n = 5). Acetylstrophanthidin (100 microM basolateral) reduced JWL-->B from 6.1 to 4.4 microliter/min/cm2 (p < 0. 05, n = 5) and abolished the PD. Amiloride (10 microM luminal) reduced JWL-->B from 5.7 to 3.7 microliter/min/cm2 (p < 0.05, n = 5) and reduced PD by 44%. Neither of these agents significantly changed JWB-->L. These data indicate that in tracheal epithelia under homeostatic conditions, JWB-->L was dominated by diffusion (Ea = 4.6 kcal/mol), whereas approximately 30% of JWL-->B was coupled to the active Na+,K+-ATPase pump (Ea = 27 kcal/mol).

Vocal Folds Detect Ionic Perturbations on the Luminal Surface: An In Vitro Investigation

“…This criterion for evaluating tissue viability was based on prior research in airway epithelia demonstrating active ion transport via the activity of Na þ K þ ATPase only at a membrane PD greater than 5 mV (lumen negative). 28,29 A membrane PD smaller than this threshold was observed in less than 7% of the vocal fold membranes. Vocal fold membranes that recorded a PD of 5 mV (lumen negative) within 5 minutes of mounting were allowed to stabilize for 45 minutes.…”

“…28,31 Exposure to ionic challenge altered resistance over time but sham or osmotic challenges did not (ANOVA interaction effect: F 5 7.73, df 5 12, 45, P ! 0.01, Figure 7).…”

Acute Nanoparticle Exposure to Vocal Folds: A Laboratory Study

“…Only epithelia with TEER exceeding 300 Ω*cm 2 were included in subsequent experiments. 19 The TEER values were measured by DataTrax software immediately prior to and following 5 hours of exposure to SWCNT or control (no SWCNT).…”

Anatomic sampling site and perfusate osmolarity effects on periosteum intrinsic permeability

“…The regulation of the charge and mass transport across biological membranes is fundamental to life, the maintenance of homeostasis between body fluid compartments and the preservation of the organism under adverse conditions. Osmosis, electro-osmosis, pressure differentials, surface tension and active ion-transportcoupled mechanisms have been proposed to control the mass flux across living materials (Phillips et al 1999;Lemaire et al 2011). Hence, the objective of this study was to test the hypothesis that periosteum permeability depends on anatomic sampling site as well as on osmolarity of the perfusate solution.…”